Lodima Archival Materials ships mat board overseas all the time. We have 4-ply and 8-ply and can cut custom sizes at no extra charge. And we can cut overmats with our computerized mat cutter. There are no minimum quantities.
See http://www.superiorarchivalmats.com/sam/index.html for more information
Our URL will change soon to LodimaArchivalMaterials
Michael A. Smith